G-rich oligonucleotide-functionalized gold nanoparticle aggregation

Guanine-rich DNA sequences commonly form helical quadruplex structures via Hoogsteen hydrogen bonds. The aggregation behavior of the nanoparticles, which are functionalized with four-guanine-terminated 27-base sequences at a nanoparticle-to-DNA ratio of 1:60, is investigated. To some extent, the guanine-quadruplex structures between the gold nanoparticles (GNPs) promote nanoparticle aggregation. However, the coordination site of the metal ion on the nanoparticle surface is partially passivated: the stability of guanine-rich DNA-GNPs is slightly lower than that of the usual DNA-GNPs, and the metal-ion specificity of nanoparticle assembly is substantially decreased. Thus, a mechanism for the aggregation of guanine-rich sequence-modified GNPs is proposed. It is possible to obtain a stable guanine-rich sequence-functionalized nanoparticle solution at high ionic strength by regulating guanine-rich DNA sequences. The controllability of guanine-rich sequence-modified nanoparticles makes the secondary structure of DNA a potentially useful candidate for DNA analysis and disease diagnostics. Figure Proposed mechanism for the aggregation of G-rich sequence-functionalized GNP Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

SERS studies of the adsorption of guanine derivatives on gold colloidal nanoparticles

Surface enhanced Raman scattering spectra of guanine, guanosine and 2'-deoxyguanosine adsorbed on gold colloidal nanoparticles were obtained. From the striking similarity of the SERS spectra of these compounds, it can be evidenced that guanosine and 2'-deoxyguanosine adsorb on gold nanoparticles through the guanine moiety. The molecular sites involved in the interaction with the gold surface are the same for the 3 compounds: the oxygen of the carbonilic group and the N(7) atom. Guanine, guanosine and 2'-deoxyguanosine adsorb on the gold substrates with a tilted orientation with respect to the metal surface. SERS data were interpreted taking into account density functional theoretical (DFT) calculations of guanine.     

Duplex dissociation of telomere DNAs induced by molecular crowding

Because of the importance of telomere DNAs, the structures of these DNAs in vivo are currently of great research interest in the medical, pharmaceutical, chemical, and industrial fields. To understand the structure of biomolecules in vivo, their properties studied in vitro are extrapolated to the in vivo condition, while the condition in a living cell is inherently molecularly crowded and a nonideal solution contains various biomolecules. We investigated the effect of molecular crowding, which is one of the most important cellular environmental conditions, on the structure and stability of the telomere and G-rich and C-rich DNAs using circular dichroism (CD) spectra, CD melting curves, and isothermal titration calorimetry (ITC). The CD spectra and CD melting curves of G-rich DNA, C-rich DNA, and the 1:1 mixture of G-rich and C-rich DNAs showed that each G-rich DNA, C-rich DNA, and the 1:1 mixture form the antiparallel G-quadruplex, I-motif, and duplex, respectively, in the noncrowding condition as previously considered. On the contrary, the G-rich and C-rich DNAs individually form the parallel G-quadruplex and I-motif, respectively, in the molecular crowding condition, and the 1:1 mixture folds into the parallel G-quadruplex and I-motif but does not form a duplex. The ITC measurements indicated that the thermodynamic stability (DeltaG degrees (20)) of the duplex formation between the G-rich and C-rich DNAs in the noncrowding condition was -10.2 kcal mol(-)(1), while only a small heat change was observed in the ITC measurements in the molecular crowding condition. These ITC results also demonstrated that the molecular crowding condition prevents any duplex formation between G-rich and C-rich DNAs. These results indicate that a structural polymorphism of the telomere DNAs is induced by molecular crowding in vivo.     

基于G-四联体的纳米探针比色检测铅离子

基于纳米探针和G-四联体建立了简便快速检测铅离子的方法. 纳米探针采用金纳米粒子自组装修饰富G寡核苷酸制得, 在铅离子存在下, 纳米探针上的富G寡核苷酸形成G-四联体, 导致纳米探针凝聚变色. 在优化条件下, 比色检测铅离子的线性范围为48~480 nmol/L, 检出限为20 nmol/L; 大多数金属离子无明显干扰, 而有明显干扰的汞离子可采用与之特异结合的寡核苷酸有效消除. 将该法成功用于环境水样中铅离子的检测, 重现性(RSD<3.0%)与回收率(98.4%~101.5%)良好.     

Characterization of G-rich and T-rich oligonucleotides using ion-pair reversed-phase high-performance liquid chromatography/tandem electrospray ionization mass spectrometry

Characteristics of G-rich and T-rich oligonucleotides were investigated to compare their retention time, total ion current (TIC) intensity, charge-state distribution and product ion using ion-pair reversed-phase high- performance liquid chromatography/tandem electrospray ionization mass spectrometry (IP-RP-HPLC/ESI-MS) at room temperature. Three commonly used mobile phases for the analysis of oligonucleotides, triethylammonium acetate (TEAA), triethylammonium bicarbonate (TEAB) and triethylammonium hexafluoroisopropanol (HFIP) have been utilized. Retention time of G-rich and T-rich oligonucleotides was significantly different in TEAA and TEAB buffer systems, while in the HFIP buffer system it was affected more by the length of oligonucleotides. On the other hand, the ESI-MS ion abundance in the HFIP buffer system was higher than that in both TEAA and TEAB buffers. The TIC intensity of T-rich oligonucleotides was much higher than that of G-rich oligonucleotides in all mobile phases. In addition, much higher charge-state fragments were observed in HFIP buffer system than that in the case of TEAA and TEAB buffer systems. Product ions of both G-rich and T-rich oligonucleotides were affected by charge state of parent ions and collision energy.     

Expanding the Topological Landscape by a G-Column Flip of a Parallel G-Quadruplex

Canonical G-quadruplexes can adopt a variety of different topologies depending on the arrangement of propeller, lateral, or diagonal loops connecting the four G-columns. A novel intramolecular G-quadruplex structure is derived through inversion of the last G-tract of a three-layered parallel fold, associated with the transition of a single propeller into a lateral loop. The resulting (3+1) hybrid fold features three syn⋅anti⋅anti⋅anti G-tetrads with a 3’-terminal all-syn G-column. Although the ability of forming a duplex stem-loop between G-tracts seems beneficial for a propeller-to-lateral loop rearrangement, unmodified G-rich sequences resist folding into the new (3+1) topology. However, refolding can be driven by the incorporation of syn-favoring guanosine analogues into positions of the fourth G-stretch. The presented hybrid-type G-quadruplex structure as determined by NMR spectroscopy may provide for an additional scaffold in quadruplex-based technologies.     

Quantum dot nanocrystals having guanosine imprinted nanoshell for DNA recognition

Molecular imprinted polymers (MIPs) as a recognition element for sensors are increasingly of interest and MIP nanoparticles have started to appear in the literature. In this study, we have proposed a novel thiol ligand-capping method with polymerizable methacryloylamido-cysteine (MAC) attached to CdS quantum dots (QDs), reminiscent of a self-assembled monolayer and have reconstructed surface shell by synthetic host polymers based on molecular imprinting method for DNA recognition. In this method, methacryloylamidohistidine-platinium (MAH-Pt(II)) is used as a new metal-chelating monomer via metal coordination-chelation interactions and guanosine templates of DNA. Nanoshell sensors with guanosine templates give a cavity that is selective for guanosine and its analogues. The guanosine can simultaneously chelate to Pt(II) metal ion and fit into the shape-selective cavity. Thus, the interaction between Pt(II) ion and free coordination spheres has an effect on the binding ability of the CdS QD nanosensor. The binding affinity of the guanosine imprinted nanocrystals has investigated by using the Langmuir and Scatchard methods, and experiments have shown the shape-selective cavity formation with O6 and N7 of a guanosine nucleotide (K(a) = 4.841x10(6) mol L(-1)) and a free guanine base (K(a) = 0.894x10(6) mol L(-1)). Additionally, the guanosine template of the nanocrystals is more favored for single stranded DNA compared to double stranded DNA.     

Hydrogel-templated growth of large gold nanoparticles: synthesis of thermally responsive hydrogel-nanoparticle composites

In this paper, we describe a unique strategy for preparing discrete composite nanoparticles consisting of a large gold core (60-150 nm in diameter) surrounded by a thermally responsive nontoxic hydrogel polymer derived from the polymerization of N-isopropylacrylamide (NIPAM) or a mixture of NIPAM and acrylic acid. We synthesize these composite nanoparticles at room temperature by inducing the growth of gold nanoparticles in the presence of preformed spherical hydrogel particles. This new method allows precise control of the size of the encapsulated gold cores (tunable between 60 and 150 nm) and affords composite nanoparticles possessing diameters ranging from as small as 200 nm to as large as 550 nm. Variable-temperature studies show that the hydrodynamic diameter of these composite nanoparticles shrinks dramatically when the temperature is increased above the lower critical solution temperature (LCST); correspondingly, when the temperature is lowered below the LCST, the hydrodynamic diameter expands to its original size. These composite nanoparticles are being targeted for use as optically modulated drug-delivery vehicles that undergo volume changes upon exposure to light absorbed by the gold nanoparticle core.     

Epoxide assisted sol-gel synthesis of rutile NixTi1-3xSb2xO2 solid solution nanoparticles

Rutile Ni _x Ti_1-3x Sb_2x O₂ solid solution nanoparticles were synthesized by a sol-gel route using propylene oxide as a gelation agent. Titanium oxide nanopowder and 12% TiCl₃ solution were used as the source for titanium to investigate the influence of the titanium precursors on the formation of the target materials. It was found that the nanoparticles prepared using 12% TiCl₃ solution showed a much lower phase formation temperature (700°C) as compared to those prepared from TiO₂ nanoparticles (1000°C). This lower phase formation temperature allowed a substantial reduction of the aggregation of the particles during calcination leading to the formation of nearly mono-dispersed nanoparticles of about 20 nm. The results of this work show that the epoxide assisted sol-gel method is capable to produce titanium-based ternary oxide solid solution nanoparticles, owing to the formation of a highly homogeneous precursor gel intermediate.     

Dual magnetic-/temperature-responsive nanoparticles for microfluidic separations and assays

A stimuli-responsive magnetic nanoparticle system for diagnostic target capture and concentration has been developed for microfluidic lab card settings. Telechelic poly(N-isopropylacrylamide) (PNIPAAm) polymer chains were synthesized with dodecyl tails at one end and a reactive carboxylate at the opposite end by the reversible addition fragmentation transfer technique. These PNIPAAm chains self-associate into nanoscale micelles that were used as dimensional confinements to synthesize the magnetic nanoparticles. The resulting superparamagnetic nanoparticles exhibit a gamma-Fe2O3 core ( approximately 5 nm) with a layer of carboxylate-terminated PNIPAAm chains as a corona on the surface. The carboxylate group was used to functionalize the magnetic nanoparticles with biotin and subsequently with streptavidin. The functionalized magnetic nanoparticles can be reversibly aggregated in solution as the temperature is cycled through the PNIPAAm lower critical solution temperature (LCST). While the magnetophoretic mobility of the individual nanoparticles below the LCST is negligible, the aggregates formed above the LCST are large enough to respond to an applied magnetic field. The magnetic nanoparticles can associate with biotinylated targets as individual particles, and then subsequent application of a combined temperature increase and magnetic field can be used to magnetically separate the aggregated particles onto the poly(ethylene glycol)-modified polydimethylsiloxane channel walls of a microfluidic device. When the magnetic field is turned off and the temperature is reversed, the captured aggregates redisperse into the channel flow stream for further downstream processing. The dual magnetic- and temperature-responsive nanoparticles can thus be used as soluble reagents to capture diagnostic targets at a controlled time point and channel position. They can then be isolated and released after the nanoparticles have captured target molecules, overcoming the problem of low magnetophoretic mobility of the individual particle while retaining the advantages of a high surface to volume ratio and faster diffusive properties during target capture.     

Preparation of thermosensitive polymer nanoparticles by protein-mimetic cross-linking

Thermosensitive nanoparticles were prepared by mimicking protein folding where polymer aggregates were formed by precipitation of thermosensitive polymer chains followed by disulfide formation of their thiol groups. N-Isopropylacrylamide (NIPAM) and methacryloxy succinimide (SuMA) were co-polymerized and then cysteamine was allowed to react with succinimide moieties of the polymer to render thiol moieties. A polymer aqueous solution precipitated to form nano-sized aggregates by increasing temperature above its lower critical solution temperature (LCST), and their sizes were monodispersed and tunable by the polymer concentration. The aggregates were cross-linked to produce nanoparticles by oxidation of thiol groups in a manner similar to formation of a disulfide bond of protein. As a result, the cross-linked nanoparticles exhibited swelling by decreasing temperature below the LCST of the copolymer. Fluorescein and bovine serum albumin (BSA) were chosen as a small and a large substance, respectively, and were encapsulated into the swollen nanoparticles at 25?°C. Fluorescein was rapidly released from both swollen and shrunken nanoparticles. Although BSA exhibited little release at any temperatures, it was released from nanoparticles by adding the reducing agent to dissociate the disulfide cross-linking and incubating below the LCST.     

Formation of gold@polymer core-shell particles and gold particle clusters on a template of thermoresponsive and pH-responsive coordination triblock copolymer

Template synthesis of various morphological gold colloidal nanoparticles using a thermoresponsive and pH-responsive coordination triblock copolymer of poly(ethylene glycol)-b-poly(4-vinylpyridine)-b-poly(N-isopropylacrylamide) is studied. The template morphology of the thermoresponsive and pH-responsive coordination triblock copolymer, which can be tuned by simply changing the pH or temperature of the triblock copolymer aqueous solution, ranges from single chains to core-corona micelles and further to micellar clusters. Various morphological gold colloidal nanoparticles such as discrete gold nanoparticles, gold@polymer core-shell nanoparticles, and gold nanoparticle clusters are synthesized on the corresponding template of the triblock copolymer by first coordination with gold ions and then reduction by NaBH4. All three resultant gold colloidal nanoparticles are stable in aqueous solution, and their sizes are 2, 10, and 7 nm, respectively. The gold@polymer core-shell nanoparticles are thermoresponsive. The gold nanoparticle cluster has a novel structure, and each one holds about 40 single gold nanoparticles.     

Simultaneous determination of guanosine and guanosine-5'-triphosphate in biological sample using gold nanoparticles modified indium tin oxide electrode

A nanogold modified indium tin oxide (ITO) electrode was used for the simultaneous determination of guanosine and GTP at pH 7.2. The electrode exhibited an effective catalytic response towards their oxidation and lowered the oxidation potential of guanosine by ∼120 mV and GTP by ∼183 mV. Linear concentration curves were obtained for guanosine with a detection limit of 9.8 × 10⁻⁸ M and 5.5 × 10⁻⁸ M for GTP. The concentration of guanosine and GTP were also estimated in the human blood plasma samples using gold nanoparticles modified ITO electrode with good reproducibility.     

Redispersible and stable amorphous calcium phosphate nanoparticles functionalized by an organic bisphosphate

Although much effort has been focused on the preparation of stable amorphous calcium phosphate （ACP） nanoparticles in aqueous solution, the redispersibility and long-term stability of ACP nanoparticles in aqueous solution remains an unresolved problem. In this work, stable colloidal ACPs were prepared by using an organic bisphosphonate （BP） as a sterically hindered agent in aqueous solution. The harvested calcium phosphate nanoparticles were characterized by inductively coupled plasma atomic emission spectrometry （ICP-AES）, Fourier transform infrared （FTIR）, X-ray diffraction （XRD）, dynamic light scattering （DLS） and transmission electron microscopy （TEM）. ICP-AES, FTIR and XRD results suggested the particles were ACP. DLS and TEM results indicated that the size of the ACP nanoparticles were in the range of 60 nm with a spherical morphology. The resulting calcium phosphate nanoparticles retained its amorphous nature in aqueous solution for at least 6 months at room temperature due to the stabilizing effect of the organic bisphosphonate. Moreover, the surface of the ACP nanoparticles adsorbed with the organic bisphosphate used showed good redispersibility and high colloid stability both in organic and aqueous solutions.     

Stacked and continuous helical self-assemblies of guanosine monophosphates detected by vibrational circular dichroism

The aim of this study was to characterize self-assembled structures of guanosine derivatives in aqueous solutions by vibrational circular dichroism (VCD) and electronic circular dichroism (ECD). Three guanosine derivatives were studied [5'-guanosine monophosphate (GMP), diphosphate (GDP), and triphosphate (GTP)] using a broad range of concentrations and various metal/guanosine ratios. VCD was used for the first time in this field and showed itself to be a powerful method for obtaining specific structural information in solution. It can also help to determine the impact that the cations have, when added to the solution, on the versatile structures of guanine derivatives in terms of their association and disassociation. Based on the markedly different intensities and signs of the VCD signals observed for different concentrations of guanosine derivatives, we propose various structures based on guanine quartets for high guanosine concentrations and high K(+)/guanosine ratios (i.e., columnar helical organization of the quartets, which are rearranged into a continuous helix). We performed a degenerate coupled oscillator (DCO) calculation to interpret the VCD spectra obtained and how they vary during the assembly of guanosine derivatives. The calculations correctly predicted the VCD spectra and enabled us to identify the structures of the metal cation/guanosine monophosphate aggregates. ECD in the ultraviolet region was used as a diagnostic tool to characterize the studied systems and as a contact point between the previously defined structures of the guanine derivative assemblies and the molecular systems studied here. These studies revealed that the VCD technique is a powerful new method for determining the structures of optically active guanosine motifs.     

Murraya Koenigii leaf-assisted rapid green synthesis of silver and gold nanoparticles

A facile bottom-up 'green' and rapid synthetic route using Murraya Koenigii leaf extract as reducing and stabilizing agent produced silver nanoparticles at ambient conditions and gold nanoparticles at 373 K. The nanoparticles were characterized using UV-vis, transmission electron microscopy (TEM), X-ray diffraction (XRD) and FTIR analysis. This method allows the synthesis of well-dispersed silver and gold nanoparticles having size ～10 nm and ～20 nm, respectively. Silver nanoparticles with size ～10 nm having symmetric SPR band centered at 411 nm is obtained within 5 min of addition of the extract to the solution of AgNO3 at room temperature. Nearly spherical gold nanoparticles having size ～20 nm with SPR at 532 nm is obtained on adding the leaf extract to the boiling solution of HAuCl4. Crystallinity of the nanoparticles is confirmed from the high-resolution TEM images, selected area electron diffraction (SAED) and XRD patterns. From the FTIR spectra it is found that the biomolecules responsible for capping are different in gold and silver nanoparticles. A comparison of the present work with the author's earlier reports on biosynthesis is also included.     

Preparation of CuCrO2 nanoparticles with narrow size distribution by sol–gel method

Copper chromium oxide (CuCrO₂) nanoparticles were synthesized by sol–gel method. The effect of annealing temperature, duration of heat treatment and metallic ion concentration in precursor solution on the structural properties of the nanoparticles was investigated. The delafossite structure of CuCrO₂ powder was confirmed by X-ray diffractometer. It was found that the crystallite sizes as well as the size of the nanoparticles increased with annealing temperature and duration of heat treatment but decreased with metallic ion concentration. Nanoparticles’ size was obtained using particle size analyzer. The synthesized CuCrO₂ nanoparticles with 0.7 M metallic ion concentration have the lowest crystallite and particle sizes with a narrow size distribution in the range of 13.5–15.6 nm. In the presence of this metallic ion concentration, we could also produce single crystal CuCrO₂ nanoparticles. Moreover, the CuCrO₂ nanoparticles exhibit a large optical band gap that increases with metallic ion concentration. The optical band gap of the nanoparticles fabricated with 0.7 M metallic ion concentration in precursor solution is about 3.99 eV.     

RNA quadruplex-based modulation of gene expression

RNA-based modules such as riboswitches represent straightforward and simplified approaches for the regulation of gene expression, as no additional proteins are needed. G-rich sequences are known to adopt stable four-stranded structures, and such quadruplexes have been suspected to play important roles in key functions such as the control of gene expression. Here we demonstrate that RNA quadruplexes readily form in vivo. We have constructed mRNA-based G-rich elements that mask the ribosome binding site by folding into four-stranded structures. The suppression of gene expression correlates with the stability of inserted G quadruplexes. Moreover, quadruplexes with moderate stability respond to changes in temperature, thus behaving as artificial RNA thermometers. In conclusion, we introduce tuneable mRNA-based devices that enable modulation of gene expression by a predictable but thus far unknown mechanism.     

Reaction of (R)-(-)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato)platinum( II) with guanosine

The reaction of a new antitumor platinum complex, (R)-(-)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato++ +)platinum(II) (1) with guanosine at room temperature in an aqueous solution was followed by proton nuclear magnetic resonance (1H-NMR) spectroscopy and high performance liquid chromatography (HPLC) at intervals. Both techniques showed that a new compound was formed by displacement of the 1,1-cyclobutanedicarboxylate moiety of 1 with two guanosines, and its 1H-NMR spectrum and HPLC chromatogram were proved to be identical with those of [(R)-(-)-2-aminomethylpyrrolidine]bis(N7-guanosine)platinum(II) (2), which was obtained upon successive treatment of (R)-(-)-2-aminomethylpyrrolidinedichloroplatinum(II) (3) with AgNO3 and 2 mol eq of guanosine in water. The binding sites of the platinum to the two guanosine moieties in 2 were confirmed by the pH dependence of the two G-H8 signals.     

鸟嘌呤、鸟苷及其甲基化衍生物的近红外傅里叶变换表面增强拉曼光谱

本文给出了采用表面增强傅里叶变换拉曼光谱法测定的鸟嘌呤、鸟苷及其甲基化衍生物的拉曼散射。实验结果表明，采用了近红外波长的拉曼散射及傅里叶变换技术成功地获得鸟嘌呤、鸟苷及其甲基化衍生物的水溶液在较低浓度下（0．1～0．01mg／L）不受荧光干扰的拉曼光谱图，其频率与相对强度分布表明，水溶液状态下吸附在Ag膜上的鸟嘌呤（苷）及其衍生物结构中的有关振动谱带r（C＝O）、NH2和杂环上的N获得显著增强。本文对水溶液鸟嘌呤（苷）及其衍生物的FT－Raman谱带的归宿进行了讨论。